Detecting Faked IATs via Task-Switch Costs

Author

Anke Cajar (plus a few revisions: Reinhold Kliegl)

Published

August 9, 2022

1 Anke Cajar (AC): Analysis/modeling issues

Is the contrast coding appropriate?
What is currently the best method for model selection (concerning questions like: from maximal to minimal model, doing rePCA, …)? Is the stuff from the RePsychLing package and vignettes still the way to do it?
How do I make sure that the random effects structure of my selected model is really supported by the data (again, rePCA?)?
How do I decide which optimizer to use for model fitting? I heard bobyqa is supposed to be good…
It seems that the order in which I put the factors in the formula changes the outcome. How do I decide on the order (most important factor first, than second etc.?)?
Model results (model 13) don’t really fit the mean response time/switch costs plot, as part of the effects you see in the figure goes into the random effects (By chance, there were more older subjects > 45 years in the no-faking group, who had considerably longer mean response times in the baseline IAT). How do I report this in a paper? Should I plot the fixed effects from the model instead of mean response times (which I’d rather not)?

2 Background and overview

Data are from André Krügel.
Revisions and additions for SMLP2022 by Reinhold Kliegl (RK)
Revisions do not affect the main conclusion, but highlight common problems with fitting LMMs related to
- contrast specification
- convergence issue
- zero correlation parameters
Addition of new chunks illustrate
- selection of parsimonious LMM using random-effects PCA (rePCA()) and LRTs (anova())
- plotting partial effect of high-order interaction (remef())
- plotting conditional means

2.1 Data

This is data from an experiment showing that we can reliably detect whether outcomes from the Implicit Association Test (IAT) are faked by analysing task-switch costs in the combined blocks of the IAT (see next paragraph) Every participant performed two IATs: the control group performed the same normative IAT twice and the faking group was instructed to fake the second IAT by deliberately slowing down response times in the compatible block. It has been shown that switches from a target-concept word to an attribute-dimension word between consecutive trials produces stronger switch costs (i.e., response-time differences between task-repetition and task-switch trials) in the incompatible block than in the compatible block. The present data show that even after successful faking of the IAT, these switch costs are preserved (although the true compatible block became the faked incompatible block). Thus, switch costs can be used to detect IAT faking reliably and with high accuracy.

2.2 IAT and faking strategies

The IAT measures people’s implicit associations between a target concept and an attribute dimension. People have to assign consecutively presented words as fast as possible to one of four categories—two categories belong to the target concept (e.g., family vs career words) and two categories belong to the attribute dimension (e.g., male vs female words). When strongly associated concepts share the same response key in the categorization task (e.g., career and male words or family and female words), response times are usually shorter than when less associated concepts share the same response key (e.g., career and female words or family and male words). The IAT block with shorter response times is called the compatible block, whereas the block with longer response times is called the incompatible block. IAT results can be deliberately faked, most easily and reliably by slowing down response times in the actual compatible block (making it look like the incompatible block and thus reversing associations). To date, an effective and accurate method for detecting faked IATs is still missing.

3 Readme

3.1 Design

Design: 2 (B-Subj/W-Item) x 2 (W) x 2 (W) x 2 (W) factorial mixed design
N trials: 38 Subj x 20 Item x 8 W-Item x 2 repetition of items = 12160
N errors: 391 (3.2%)
N observations: 12160-391=11769

3.2 Variables

Subj: Participant ID (renamed from ID; random factor)
Item: Word ID (random factor)
Group (between-Subj/within-Item):
- No_Faking: control group, where people took the same normative IAT twice
- Faking: experimental group, where people were instructed to fake the retest IAT by slowing down response times in the compatible block
Time (within-Subj/within-Item):
- Baseline: first IAT (normative IAT)
- Retest: second IAT (normative or faked, depending on Group)
Block (within-Subj/within-Item):
- Compatible: IAT combined block with shorter response times
- Incompatible: IAT combined block with longer response times
Switch (renamed from TaskSwitch; within-Subj/within-Item):
- Yes: Switch from target concept to attribute dimension (or the other way around) from one trial to the next
- No: No switch from target concept to attribute dimension (or the other way around) from one trial to the next
rt: trial response time (DV, renamed from RT)

4 Load packages

library(arrow)
suppressWarnings(suppressMessages(library(tidyverse)))
suppressWarnings(suppressMessages(library(easystats)))
#library(summarytools)
library(lme4)
library(car)
library(GGally)
library(ellipse)

# respecting color vision deficiency
cbPalette <- c( "#0072B2", "#D55E00", "#009E73", "#CC79A7",
                "#F0E442", "#56B4E9", "#999999", "#E69F00")

5 Preprocessing

5.1 Trial data

Random factors should be factors, not integers!
RK style preferences
- Factors capitalized, continuous variables in lower case
- Subj instead of ID; prefix subject and item numbers with S and I
- Short variable names and factor levels, but respect tradeoff with mmemonic value
- Labels should be of equal length
- Hint: Leave out vowels in names and labels
See Jenny Bryan’s Naming Things

iat <- 
  read.table("./data/IAT_data.dat", header=TRUE, stringsAsFactors=TRUE) |> 
  rename("Subj" = "ID", "rt" = "RT", "Switch" = "TaskSwitch") |>
  mutate(
    Group = relevel(Group, ref="No_Faking"),
    Subj = factor(paste0("S", str_pad(Subj, width = 3, side = "left", pad = "0"))),
    Item = factor(paste0("I", str_pad(Item, width = 2, side = "left", pad = "0")))
    ) |> 
  filter(rt >= 400 & rt <= 10000) |> 
  as_tibble()

#stview(dfSummary(iat), method="render")

factor() generates alphabetic sorting of factor leveks; as_factor() sorts them by occurrence.
See IAT scoring procedure from Greenwald et al. (2003) for removal of rt outliers.

5.2 Subject data

Rename variables
Convert types
Add membership in experimental Group
Replace missing age with median and missing Gender with mode

sinfo <- 
  read.table("./data/IAT_subj.dat", header=TRUE, stringsAsFactors=FALSE) |> 
  rename(Subj=ID, age=Age) |> 
  mutate(Subj = factor(paste0("S", str_pad(Subj, width = 3, side = "left", pad = "0"))))

sGroup <- iat |> count(Subj, Group)  

sinfo <- 
  sinfo |> 
  left_join(sGroup, by="Subj") |> 
   mutate(age = ifelse(is.na(age),median(age, na.rm = TRUE), age),
          Gender = as_factor(ifelse(is.na(Gender), "female", Gender)))

#stview(dfSummary(sinfo), method="render")

5.3 Item data

Item categories:
- Task (target concept vs. attribute)
- Valence (positive vs. negative words, included as nested within levels of Task

items <- 
  read.table("./data/IAT_item.dat", header=TRUE, encoding = "UTF-8") |> 
  mutate(
    Task = as_factor(if_else(Item <=10, "target", "attribute")),
    Valence = as_factor(if_else(Item <= 5 | (Item >=11 & Item <= 15), "+", "-")),
    Item = factor(paste0("I", str_pad(Item, width = 2, side = "left", pad = "0")))
  )

#stview(dfSummary(items), method="render")

5.4 Combine data

The dataframe will be used in analyses with MixedModels.jl in Julia.

dat <- 
  iat |> 
  left_join(sinfo, by=c( "Group", "Subj")) |> 
  left_join(items, by="Item") |> 
  select(Subj, Gender, age, Item, Word, Task, Valence, Group, Time, Block, Switch, rt)

write_feather(dat, "./data/Cajar_IAT.arrow")

Separate files for data, subject info, and item info are easier to maintain and are preferred for storage in a public repository. The information can be combined as needed. The redundant format of one integrated file chosen here is to facilitate transition to working with Julia MixedModels.jl at SMLP2022.

5.5 Check distribution of rt’s

lambdaList <- MASS::boxcox(lm(rt ~ Group*Time*Block*Switch, data=dat))

(lambda <- lambdaList$x[which.max(lambdaList$y)])

[1] -0.9090909

hist(1000/dat$rt)

dat$speed <- 1000/dat$rt

The check suggests reciprocal transformation of rt, that is to use speed.

6 Plot switch costs

RK: Put Time on blocks of x-axis?

switch_costs <- dat|> 
  group_by(Time, Group, Block, Switch)|>
  summarise(M = mean(rt), SD=sd(rt), N=n(), SE=SD/sqrt(N))

`summarise()` has grouped output by 'Time', 'Group', 'Block'. You can override
using the `.groups` argument.

fig_rt <- ggplot(switch_costs, aes(x=Switch, y=M, color=Block)) +
  geom_point(size=2) +
  geom_line(size=0.7, aes(group=Block)) +
  geom_errorbar(aes(ymin=M-2*SE, ymax=M+2*SE), width=.1, size=0.7) +
  facet_grid(Group~Time) +
  scale_color_manual("Block", values=cbPalette) +
  labs(x="Task switch", y="Response time [ms]") +
  theme_bw(base_size=13)
print(fig_rt)

7 AC’s model selection (revised)

This section reproduces logic of the original model selection, but where necessary with corrected LMM syntax.

7.1 Define contrasts

#ctable(dat$Group, dat$Time)
#ctable(dat$Switch, dat$Block)

contrasts(dat$Group)  <- contr.treatment(2)
contrasts(dat$Time)   <- contr.treatment(2)
contrasts(dat$Block)  <- contr.sum(2)/-2
contrasts(dat$Switch) <- contr.sum(2)/-2

RK:

If you mix treatment and sum contrasts in the context of multifactorial experiments you really need to know what the coefficients are estimating. They are not representing the usual ANOVA main effects and interactions.
The contrasts are not orthogonal. This means you are bound to lose statistical power, except for contrasts that map directly on your hypotheses.
For hypothesis-guided contrast specification (recommended!) it may be better to explicitly specify the model matrix, rather than relying on a mixture of canned contrasts.
In the revision I use sum contrasts. They are orthogonal when all factors of have two levels. A direct comparison of the revised selected LMM model13 with the one based on treatment contrasts is provided in the Appendix.
Order of factor levels. The order of factor levels is relevant for figures and tables. I prefer time and difficulty shown in a left-to-right or top-to-bottom order. The order chosen here is in agreement with this preference:
Order of factor levels also determines the signs of effects estimated in LMMs – unless explicitly specified. In general, I prefer a specification that yields positive effects, but order by time and difficulty may generate a conflict in this respect.
For sum contrasts division by (-2) yields estimates of the difference between levels (instead of differences from Grand Mean) and the sign of the effects is reversed (i.e., Switch: yes - no; Block: incompatible - compaible). The division by 2 is strongly discouraged by Douglas Bates because indicators for higher order interaction terms become very small. Since we analyze response speed these effects are expected to be negative. Therefore, for my own model selection (see below), I will not divide by 2 and I will not reverse the direction of effects for sum contrasts.

7.2 Models that do not (or did not) converge

AC: I tried model selection by starting with the maximal model and working my way down to the minimal model.
RK. Some convergence issues were due to false positives. Double-bar syntax does not work with factors; you need to convert to indicator variables – see next chunk.

mm <- model.matrix(~ 1 + Group*Time*Block*Switch, data=dat)
gr <- mm[,2]
tm <- mm[,3]
bl <- mm[,4]
sw <- mm[,5]

RK: Always use control=lmerControl(calc.derivs=FALSE). Most convergence warnings are false positives.
RK: Group is a within-item factor; added as item-related VC.
RK: Save objects that take a long time to fit to be available for quick load later.
RK: Add LRTs for model comparisons (i.e., anova())

f1 <- "./fits/model1.rda"
if(!file.exists(f1)){
  model1 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                        (1 +       Time*Block*Switch|Subj) + 
                        (1 + Group*Time*Block*Switch|Item), 
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
  save(model1, file=f1)
} else load(f1)

summary(rePCA(model1))  # definitely overparameterized in Item, probably also in Subj

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]    [,5]    [,6]    [,7]
Standard deviation     0.7890 0.5034 0.4059 0.19518 0.17993 0.10328 0.06773
Proportion of Variance 0.5527 0.2250 0.1462 0.03382 0.02874 0.00947 0.00407
Cumulative Proportion  0.5527 0.7777 0.9239 0.95772 0.98646 0.99593 1.00000
                            [,8]
Standard deviation     7.902e-05
Proportion of Variance 0.000e+00
Cumulative Proportion  1.000e+00

$Item
Importance of components:
                         [,1]   [,2]    [,3]    [,4]    [,5]    [,6]     [,7]
Standard deviation     0.7788 0.3155 0.21114 0.15068 0.13482 0.05255 0.002507
Proportion of Variance 0.7636 0.1253 0.05613 0.02858 0.02288 0.00348 0.000010
Cumulative Proportion  0.7636 0.8889 0.94505 0.97363 0.99651 0.99999 0.999990
                          [,8]     [,9]     [,10]     [,11]     [,12]     [,13]
Standard deviation     0.00149 0.001134 0.0006525 0.0004157 0.0001883 8.655e-05
Proportion of Variance 0.00000 0.000000 0.0000000 0.0000000 0.0000000 0.000e+00
Cumulative Proportion  1.00000 1.000000 1.0000000 1.0000000 1.0000000 1.000e+00
                           [,14]     [,15] [,16]
Standard deviation     6.228e-05 8.605e-06     0
Proportion of Variance 0.000e+00 0.000e+00     0
Cumulative Proportion  1.000e+00 1.000e+00     1

VarCorr(model1)

 Groups   Name                        Std.Dev. Corr                       
 Subj     (Intercept)                 0.176132                            
          Time2                       0.137084 -0.376                     
          Block1                      0.081552 -0.249  0.078              
          Switch1                     0.067353 -0.120  0.345 -0.260       
          Time2:Block1                0.251775  0.282 -0.814 -0.337  0.060
          Time2:Switch1               0.030423  0.311 -0.768 -0.175 -0.146
          Block1:Switch1              0.106526 -0.247  0.015  0.621 -0.219
          Time2:Block1:Switch1        0.140614  0.125  0.614 -0.244  0.450
 Item     (Intercept)                 0.033383                            
          Group2                      0.013518 -0.842                     
          Time2                       0.022327 -0.782  0.710              
          Block1                      0.052107  0.193  0.028 -0.047       
          Switch1                     0.029923 -0.101  0.554  0.263 -0.110
          Group2:Time2                0.018714  0.370 -0.312 -0.727  0.412
          Group2:Block1               0.056356 -0.595  0.553  0.693 -0.180
          Time2:Block1                0.083064 -0.546  0.187  0.360 -0.814
          Group2:Switch1              0.054139  0.010 -0.314 -0.200  0.268
          Time2:Switch1               0.021431  0.706 -0.847 -0.648  0.089
          Block1:Switch1              0.115563 -0.139  0.398  0.021 -0.524
          Group2:Time2:Block1         0.089753  0.859 -0.718 -0.651  0.328
          Group2:Time2:Switch1        0.059344  0.102  0.155 -0.034 -0.502
          Group2:Block1:Switch1       0.136108 -0.023 -0.256 -0.159  0.318
          Time2:Block1:Switch1        0.141394 -0.100 -0.105 -0.031  0.576
          Group2:Time2:Block1:Switch1 0.166251 -0.112  0.250  0.091 -0.432
 Residual                             0.372661                            
                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
  0.596                                                                      
 -0.277  0.082                                                               
 -0.351 -0.685 -0.659                                                        
                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
 -0.367                                                                      
  0.274 -0.480                                                               
 -0.121 -0.368  0.562                                                        
 -0.776  0.413 -0.618 -0.175                                                 
 -0.554  0.235 -0.375 -0.238  0.187                                          
  0.760 -0.210  0.423  0.343 -0.850 -0.329                                   
 -0.151  0.358 -0.856 -0.703  0.367  0.491 -0.423                            
  0.721 -0.311  0.426  0.277 -0.936 -0.096  0.935 -0.265                     
 -0.740  0.375 -0.616 -0.230  0.993  0.172 -0.857  0.355 -0.950              
 -0.683  0.362 -0.453 -0.376  0.903  0.153 -0.885  0.251 -0.972  0.936       
  0.511 -0.260  0.692  0.443 -0.904 -0.064  0.862 -0.559  0.904 -0.919 -0.862

# Replace factor with indicator variables in RES
f2 <- "./fits/model2.rda"
if(!file.exists(f2)){
  model2 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                        (1 +    tm*bl*sw||Subj) + 
                        (1 + gr*tm*bl*sw||Item), 
                 data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
  save(model2, file=f2)
} else load(f2)

summary(rePCA(model2))  # Still overparameterized for Subj and Item

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]    [,5]    [,6]   [,7]
Standard deviation     0.6438 0.4638 0.3583 0.22459 0.20771 0.20340 0.1789
Proportion of Variance 0.4481 0.2326 0.1388 0.05454 0.04665 0.04473 0.0346
Cumulative Proportion  0.4481 0.6807 0.8195 0.87401 0.92066 0.96540 1.0000
                            [,8]
Standard deviation     1.109e-05
Proportion of Variance 0.000e+00
Cumulative Proportion  1.000e+00

$Item
Importance of components:
                         [,1]   [,2]    [,3]    [,4]    [,5]    [,6]    [,7]
Standard deviation     0.1322 0.1245 0.08653 0.08049 0.05687 0.04670 0.04073
Proportion of Variance 0.3207 0.2846 0.13744 0.11893 0.05936 0.04004 0.03045
Cumulative Proportion  0.3207 0.6052 0.74269 0.86162 0.92098 0.96102 0.99147
                          [,8]     [,9]     [,10]     [,11] [,12] [,13] [,14]
Standard deviation     0.02133 0.003111 0.0001934 2.714e-05     0     0     0
Proportion of Variance 0.00835 0.000180 0.0000000 0.000e+00     0     0     0
Cumulative Proportion  0.99982 1.000000 1.0000000 1.000e+00     1     1     1
                       [,15] [,16]
Standard deviation         0     0
Proportion of Variance     0     0
Cumulative Proportion      1     1

VarCorr(model2)

 Groups   Name        Std.Dev.  
 Subj     (Intercept) 1.7362e-01
 Subj.1   tm          1.3413e-01
 Subj.2   bl          7.7763e-02
 Subj.3   sw          6.6971e-02
 Subj.4   tm:bl       2.4101e-01
 Subj.5   tm:sw       4.1517e-06
 Subj.6   bl:sw       7.6147e-02
 Subj.7   tm:bl:sw    8.4081e-02
 Item     (Intercept) 2.1290e-02
 Item.1   gr          0.0000e+00
 Item.2   tm          0.0000e+00
 Item.3   bl          3.2394e-02
 Item.4   sw          7.9846e-03
 Item.5   gr:tm       0.0000e+00
 Item.6   gr:bl       1.7484e-02
 Item.7   tm:bl       3.0134e-02
 Item.8   gr:sw       0.0000e+00
 Item.9   tm:sw       0.0000e+00
 Item.10  bl:sw       4.9481e-02
 Item.11  gr:tm:bl    1.0159e-05
 Item.12  gr:tm:sw    1.5249e-02
 Item.13  gr:bl:sw    7.2407e-05
 Item.14  tm:bl:sw    4.6614e-02
 Item.15  gr:tm:bl:sw 1.1647e-03
 Residual             3.7438e-01

anova(model2, model1)   # nothing lost, but anova() is questionable for overparameterized models

Data: dat
Models:
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
model1: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 + Group * Time * Block * Switch | Item)
       npar   AIC   BIC  logLik deviance  Chisq  Df Pr(>Chisq)
model2   41 10893 11195 -5405.4    10811                      
model1  189 11061 12455 -5341.7    10683 127.56 148     0.8866

# RK: model3 is nested under model1, not model2
f3 <- "./fits/model3.rda"
if(!file.exists(f3)){
  model3 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                        (1 +       Time+Block+Switch|Subj) + 
                        (1 + Group+Time+Block+Switch|Item), 
                 data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
  save(model3, file=f3)
} else load(f3)

summary(rePCA(model3)) # Still overparameterized for Item

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]
Standard deviation     0.5202 0.3938 0.1868 0.13634
Proportion of Variance 0.5647 0.3237 0.0728 0.03879
Cumulative Proportion  0.5647 0.8884 0.9612 1.00000

$Item
Importance of components:
                         [,1]    [,2]      [,3]      [,4] [,5]
Standard deviation     0.1107 0.07231 9.347e-05 1.899e-05    0
Proportion of Variance 0.7009 0.29907 0.000e+00 0.000e+00    0
Cumulative Proportion  0.7009 1.00000 1.000e+00 1.000e+00    1

VarCorr(model3)

 Groups   Name        Std.Dev.  Corr                       
 Subj     (Intercept) 0.1760629                            
          Time2       0.1367871 -0.370                     
          Block1      0.1233587  0.119 -0.767              
          Switch1     0.0670116 -0.050  0.157  0.023       
 Item     (Intercept) 0.0300280                            
          Group2      0.0060932 -1.000                     
          Time2       0.0140124 -0.886  0.886              
          Block1      0.0343352 -0.296  0.296  0.705       
          Switch1     0.0147804  0.504 -0.504 -0.847 -0.974
 Residual             0.3805931

anova(model3, model1)  # looks like we are losing information

Data: dat
Models:
model3: speed ~ 1 + Group * Time * Block * Switch + (1 + Time + Block + Switch | Subj) + (1 + Group + Time + Block + Switch | Item)
model1: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 + Group * Time * Block * Switch | Item)
       npar   AIC   BIC  logLik deviance Chisq  Df Pr(>Chisq)    
model3   42 11130 11440 -5523.3    11046                         
model1  189 11061 12455 -5341.7    10683 363.2 147  < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# RK: model4 is nested under model1 and model2. Need indicator variables!
model4 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                        (1 +    tm+bl+sw||Subj) + 
                        (1 + gr+tm+bl+sw||Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))

boundary (singular) fit: see help('isSingular')

summary(rePCA(model4)) # Still overparameterized for Item

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]
Standard deviation     0.4560 0.3539 0.3242 0.17605
Proportion of Variance 0.4431 0.2669 0.2240 0.06605
Cumulative Proportion  0.4431 0.7100 0.9339 1.00000

$Item
Importance of components:
                          [,1]    [,2]    [,3]      [,4] [,5]
Standard deviation     0.08934 0.05514 0.02785 3.224e-05    0
Proportion of Variance 0.67653 0.25773 0.06574 0.000e+00    0
Cumulative Proportion  0.67653 0.93426 1.00000 1.000e+00    1

VarCorr(model4)

 Groups   Name        Std.Dev.  
 Subj     (Intercept) 1.7361e-01
 Subj.1   tm          1.3475e-01
 Subj.2   bl          1.2344e-01
 Subj.3   sw          6.7031e-02
 Item     (Intercept) 2.0996e-02
 Item.1   gr          1.2275e-05
 Item.2   tm          0.0000e+00
 Item.3   bl          3.4017e-02
 Item.4   sw          1.0604e-02
 Residual             3.8075e-01

anova(model4, model1)  # loss of information

Data: dat
Models:
model4: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item))
model1: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 + Group * Time * Block * Switch | Item)
       npar   AIC   BIC  logLik deviance  Chisq  Df Pr(>Chisq)    
model4   26 11138 11330 -5543.2    11086                          
model1  189 11061 12455 -5341.7    10683 403.09 163  < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

anova(model4, model2)  # loss of information

Data: dat
Models:
model4: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item))
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
       npar   AIC   BIC  logLik deviance  Chisq Df Pr(>Chisq)    
model4   26 11138 11330 -5543.2    11086                         
model2   41 10893 11195 -5405.4    10811 275.53 15  < 2.2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# RK: model5 is nested under model1
model5 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                      (1 +       Time*Block*Switch|Subj) + (1|Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))

boundary (singular) fit: see help('isSingular')

summary(rePCA(model5)) # Still overparameterized for Subj

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]   [,5]    [,6]    [,7]
Standard deviation     0.7823 0.4970 0.4001 0.19581 0.1729 0.10144 0.07501
Proportion of Variance 0.5547 0.2240 0.1451 0.03475 0.0271 0.00933 0.00510
Cumulative Proportion  0.5547 0.7786 0.9237 0.95847 0.9856 0.99490 1.00000
                            [,8]
Standard deviation     8.059e-06
Proportion of Variance 0.000e+00
Cumulative Proportion  1.000e+00

$Item
Importance of components:
                          [,1]
Standard deviation     0.05655
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model5)

 Groups   Name                 Std.Dev. Corr                              
 Subj     (Intercept)          0.176308                                   
          Time2                0.136569 -0.372                            
          Block1               0.080339 -0.254  0.083                     
          Switch1              0.067402 -0.127  0.330 -0.255              
          Time2:Block1         0.251496  0.280 -0.815 -0.335  0.078       
          Time2:Switch1        0.029706  0.320 -0.723 -0.189 -0.136  0.550
          Block1:Switch1       0.103763 -0.256  0.029  0.646 -0.203 -0.288
          Time2:Block1:Switch1 0.139262  0.133  0.612 -0.258  0.438 -0.348
 Item     (Intercept)          0.021201                                   
 Residual                      0.374870                                   
              
              
              
              
              
              
              
  0.027       
 -0.657 -0.634

anova(model5, model1)  # loss of information

Data: dat
Models:
model5: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 | Item)
model1: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 + Group * Time * Block * Switch | Item)
       npar   AIC   BIC  logLik deviance  Chisq  Df Pr(>Chisq)
model5   54 10853 11251 -5372.4    10745                      
model1  189 11061 12455 -5341.7    10683 61.553 135          1

# RK: model6 is nested under model2. Need indicator variables!
model6 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                      (1 + tm*bl*sw||Subj) + (1|Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model6))  # Still overparameterized for Subj

$Subj
Importance of components:
                         [,1]   [,2]   [,3]   [,4]    [,5]    [,6]    [,7]
Standard deviation     0.6411 0.4629 0.3572 0.2321 0.20620 0.19928 0.17866
Proportion of Variance 0.4463 0.2327 0.1386 0.0585 0.04617 0.04312 0.03466
Cumulative Proportion  0.4463 0.6790 0.8175 0.8761 0.92222 0.96534 1.00000
                            [,8]
Standard deviation     0.0003795
Proportion of Variance 0.0000000
Cumulative Proportion  1.0000000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05681
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model6)

 Groups   Name        Std.Dev.  
 Subj     (Intercept) 0.17370466
 Subj.1   tm          0.13404300
 Subj.2   bl          0.07737078
 Subj.3   sw          0.06703647
 Subj.4   tm:bl       0.24055688
 Subj.5   tm:sw       0.00014238
 Subj.6   bl:sw       0.07477324
 Subj.7   tm:bl:sw    0.08709669
 Item     (Intercept) 0.02131672
 Residual             0.37521649

anova(model6, model2)   # No loss of information with removing item-related VCs (except for GM)

Data: dat
Models:
model6: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + (1 | Item)
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
       npar   AIC   BIC  logLik deviance  Chisq Df Pr(>Chisq)
model6   26 10876 11068 -5412.2    10824                     
model2   41 10893 11195 -5405.4    10811 13.443 15     0.5681

# RK: model7 is nested under model5
model7 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                     (1 + Time+Block+Switch|Subj) + (1|Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model7))  # looking good, but ...

$Subj
Importance of components:
                         [,1]   [,2]    [,3]    [,4]
Standard deviation     0.5192 0.3930 0.18693 0.13491
Proportion of Variance 0.5649 0.3237 0.07323 0.03814
Cumulative Proportion  0.5649 0.8886 0.96186 1.00000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05499
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model7)

 Groups   Name        Std.Dev. Corr                
 Subj     (Intercept) 0.175990                     
          Time2       0.136619 -0.370              
          Block1      0.123200  0.119 -0.768       
          Switch1     0.067065 -0.052  0.160  0.025
 Item     (Intercept) 0.020960                     
 Residual             0.381140

anova(model7, model5, model1)  # much loss of information

Data: dat
Models:
model7: speed ~ 1 + Group * Time * Block * Switch + (1 + Time + Block + Switch | Subj) + (1 | Item)
model5: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 | Item)
model1: speed ~ 1 + Group * Time * Block * Switch + (1 + Time * Block * Switch | Subj) + (1 + Group * Time * Block * Switch | Item)
       npar   AIC   BIC  logLik deviance   Chisq  Df Pr(>Chisq)    
model7   28 11117 11323 -5530.5    11061                           
model5   54 10853 11251 -5372.4    10745 316.048  26     <2e-16 ***
model1  189 11061 12455 -5341.7    10683  61.553 135          1    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# RK: model8 is nested under model6. Need indicator variables!
model8 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                      (1 + tm+bl+sw||Subj) + (1|Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model8))  # looking good, but ...

$Subj
Importance of components:
                         [,1]   [,2]   [,3]    [,4]
Standard deviation     0.4554 0.3533 0.3236 0.17584
Proportion of Variance 0.4433 0.2668 0.2238 0.06608
Cumulative Proportion  0.4433 0.7101 0.9339 1.00000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05499
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model8)

 Groups   Name        Std.Dev.
 Subj     (Intercept) 0.173582
 Subj.1   tm          0.134673
 Subj.2   bl          0.123354
 Subj.3   sw          0.067023
 Item     (Intercept) 0.020959
 Residual             0.381157

anova(model8, model6, model2) # ... loss of information with removal of Subj-related interaction VCs

Data: dat
Models:
model8: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj)) + (1 | Item)
model6: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + (1 | Item)
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
       npar   AIC   BIC  logLik deviance   Chisq Df Pr(>Chisq)    
model8   22 11138 11300 -5547.1    11094                          
model6   26 10876 11068 -5412.2    10824 269.891  4     <2e-16 ***
model2   41 10893 11195 -5405.4    10811  13.443 15     0.5681    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# RK: model 9 is nester under model8. Need indicator variables!
model9 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                      (1 + tm+sw||Subj) + (1|Item), 
               data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model9))  # looking good, but ...

$Subj
Importance of components:
                         [,1]   [,2]    [,3]
Standard deviation     0.4495 0.3491 0.17176
Proportion of Variance 0.5717 0.3448 0.08347
Cumulative Proportion  0.5717 0.9165 1.00000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05358
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model9)

 Groups   Name        Std.Dev.
 Subj     (Intercept) 0.173581
 Subj.1   tm          0.134808
 Subj.2   sw          0.066325
 Item     (Intercept) 0.020690
 Residual             0.386154

anova(model9, model8, model6, model2) # ... there is reliable Subj-related VC for Block

Data: dat
Models:
model9: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + sw | Subj)) + (1 | Item)
model8: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj)) + (1 | Item)
model6: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + (1 | Item)
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
       npar   AIC   BIC  logLik deviance   Chisq Df Pr(>Chisq)    
model9   21 11355 11510 -5656.6    11313                          
model8   22 11138 11300 -5547.1    11094 219.027  1     <2e-16 ***
model6   26 10876 11068 -5412.2    10824 269.891  4     <2e-16 ***
model2   41 10893 11195 -5405.4    10811  13.443 15     0.5681    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# RK: model10 is nested under model9. Need indicator variables!
model10 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                       (1 + tm||Subj) + (1|Item),
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE) )
summary(rePCA(model10))

$Subj
Importance of components:
                         [,1]   [,2]
Standard deviation     0.4483 0.3478
Proportion of Variance 0.6242 0.3758
Cumulative Proportion  0.6242 1.0000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05382
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model10)

 Groups   Name        Std.Dev.
 Subj     (Intercept) 0.173744
 Subj.1   tm          0.134813
 Item     (Intercept) 0.020858
 Residual             0.387566

anova(model10, model9, model8, model6, model2)

Data: dat
Models:
model10: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj)) + (1 | Item)
model9: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + sw | Subj)) + (1 | Item)
model8: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj)) + (1 | Item)
model6: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + (1 | Item)
model2: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj) + (0 + bl | Subj) + (0 + sw | Subj) + (0 + tm:bl | Subj) + (0 + tm:sw | Subj) + (0 + bl:sw | Subj) + (0 + tm:bl:sw | Subj)) + ((1 | Item) + (0 + gr | Item) + (0 + tm | Item) + (0 + bl | Item) + (0 + sw | Item) + (0 + gr:tm | Item) + (0 + gr:bl | Item) + (0 + tm:bl | Item) + (0 + gr:sw | Item) + (0 + tm:sw | Item) + (0 + bl:sw | Item) + (0 + gr:tm:bl | Item) + (0 + gr:tm:sw | Item) + (0 + gr:bl:sw | Item) + (0 + tm:bl:sw | Item) +      (0 + gr:tm:bl:sw | Item))
        npar   AIC   BIC  logLik deviance   Chisq Df Pr(>Chisq)    
model10   20 11394 11541 -5677.0    11354                          
model9    21 11355 11510 -5656.6    11313  40.672  1    1.8e-10 ***
model8    22 11138 11300 -5547.1    11094 219.027  1    < 2e-16 ***
model6    26 10876 11068 -5412.2    10824 269.891  4    < 2e-16 ***
model2    41 10893 11195 -5405.4    10811  13.443 15     0.5681    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# ... there is reliable Subj-related VC for Switch

# RK: model11 is above model10. Need indicator variables!
model11 <- lmer(speed ~ 1 + Group*Time*Block*Switch + 
                      (1 + tm||Subj) + (1 + tm||Item),
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))

boundary (singular) fit: see help('isSingular')

summary(rePCA(model11)) # overparameterized

$Subj
Importance of components:
                         [,1]   [,2]
Standard deviation     0.4483 0.3478
Proportion of Variance 0.6242 0.3758
Cumulative Proportion  0.6242 1.0000

$Item
Importance of components:
                          [,1] [,2]
Standard deviation     0.05382    0
Proportion of Variance 1.00000    0
Cumulative Proportion  1.00000    1

VarCorr(model11)

 Groups   Name        Std.Dev.
 Subj     (Intercept) 0.173748
 Subj.1   tm          0.134807
 Item     (Intercept) 0.020859
 Item.1   tm          0.000000
 Residual             0.387566

anova(model10, model11) # No evidence for Item-related VC for Time

Data: dat
Models:
model10: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj)) + (1 | Item)
model11: speed ~ 1 + Group * Time * Block * Switch + ((1 | Subj) + (0 + tm | Subj)) + ((1 | Item) + (0 + tm | Item))
        npar   AIC   BIC logLik deviance Chisq Df Pr(>Chisq)
model10   20 11394 11541  -5677    11354                    
model11   21 11396 11551  -5677    11354     0  1          1

7.3 Minimal model works

RK: As shown above, many other models also converge! Some of them were discarded due to false positive convergence errors with default setting of control=lmerControl(calc.derivs=TRUE).

model12 <- lmer(speed ~ 1 + Group*Time*Block*Switch + (1|Subj) + (1|Item), 
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model12))

$Subj
Importance of components:
                         [,1]
Standard deviation     0.4157
Proportion of Variance 1.0000
Cumulative Proportion  1.0000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05205
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model12)

 Groups   Name        Std.Dev.
 Subj     (Intercept) 0.163644
 Item     (Intercept) 0.020488
 Residual             0.393624

AC: Surprisingly, this one also works (same as model7, but with different order of factors):

model13 <- lmer(speed ~ 1 + Group*Time*Switch*Block + 
                       (1 + Time+Switch+Block|Subj) + (1|Item), 
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
summary(rePCA(model13))

$Subj
Importance of components:
                         [,1]   [,2]    [,3]    [,4]
Standard deviation     0.5191 0.3930 0.18688 0.13493
Proportion of Variance 0.5649 0.3238 0.07321 0.03816
Cumulative Proportion  0.5649 0.8886 0.96184 1.00000

$Item
Importance of components:
                          [,1]
Standard deviation     0.05497
Proportion of Variance 1.00000
Cumulative Proportion  1.00000

VarCorr(model13)

 Groups   Name        Std.Dev. Corr                
 Subj     (Intercept) 0.175975                     
          Time2       0.136613 -0.370              
          Switch1     0.067048 -0.052  0.161       
          Block1      0.123195  0.119 -0.768  0.025
 Item     (Intercept) 0.020951                     
 Residual             0.381140

print(summary(model13))

Linear mixed model fit by maximum likelihood  ['lmerMod']
Formula: speed ~ 1 + Group * Time * Switch * Block + (1 + Time + Switch +  
    Block | Subj) + (1 | Item)
   Data: dat
Control: lmerControl(calc.derivs = FALSE)

     AIC      BIC   logLik deviance df.resid 
 11116.9  11323.4  -5530.5  11060.9    11741 

Scaled residuals: 
    Min      1Q  Median      3Q     Max 
-3.9956 -0.6391  0.0143  0.6817  3.7502 

Random effects:
 Groups   Name        Variance  Std.Dev. Corr             
 Subj     (Intercept) 0.0309672 0.17598                   
          Time2       0.0186630 0.13661  -0.37            
          Switch1     0.0044955 0.06705  -0.05  0.16      
          Block1      0.0151770 0.12319   0.12 -0.77  0.02
 Item     (Intercept) 0.0004389 0.02095                   
 Residual             0.1452677 0.38114                   
Number of obs: 11769, groups:  Subj, 38; Item, 20

Fixed effects:
                             Estimate Std. Error t value
(Intercept)                  1.421067   0.041252  34.448
Group2                       0.058149   0.057958   1.003
Time2                        0.043927   0.032899   1.335
Switch1                     -0.398428   0.020889 -19.073
Block1                      -0.279961   0.031592  -8.862
Group2:Time2                -0.189745   0.046517  -4.079
Group2:Switch1               0.021271   0.029511   0.721
Time2:Switch1               -0.004223   0.020011  -0.211
Group2:Block1               -0.003972   0.044660  -0.089
Time2:Block1                 0.022783   0.019986   1.140
Switch1:Block1              -0.260199   0.028239  -9.214
Group2:Time2:Switch1         0.059655   0.028242   2.112
Group2:Time2:Block1          0.500590   0.028214  17.743
Group2:Switch1:Block1        0.046294   0.039867   1.161
Time2:Switch1:Block1         0.039553   0.039989   0.989
Group2:Time2:Switch1:Block1 -0.122949   0.056450  -2.178


Correlation matrix not shown by default, as p = 16 > 12.
Use print(summary(model13), correlation=TRUE)  or
    vcov(summary(model13))        if you need it

anova(model7, model13)

Data: dat
Models:
model7: speed ~ 1 + Group * Time * Block * Switch + (1 + Time + Block + Switch | Subj) + (1 | Item)
model13: speed ~ 1 + Group * Time * Switch * Block + (1 + Time + Switch + Block | Subj) + (1 | Item)
        npar   AIC   BIC  logLik deviance Chisq Df Pr(>Chisq)
model7    28 11117 11323 -5530.5    11061                    
model13   28 11117 11323 -5530.5    11061     0  0

compare_models(model7, model13)

Parameter                         |                   model7 |                  model13
---------------------------------------------------------------------------------------
(Intercept)                       |      1.42 ( 1.34,  1.50) |      1.42 ( 1.34,  1.50)
Group2                            |      0.06 (-0.06,  0.17) |      0.06 (-0.06,  0.17)
Time2                             |      0.04 (-0.02,  0.11) |      0.04 (-0.02,  0.11)
Block1                            |     -0.28 (-0.34, -0.22) |     -0.28 (-0.34, -0.22)
Switch1                           |     -0.40 (-0.44, -0.36) |     -0.40 (-0.44, -0.36)
Group2 * Time2                    |     -0.19 (-0.28, -0.10) |     -0.19 (-0.28, -0.10)
Group2 * Block1                   | -3.97e-03 (-0.09,  0.08) | -3.97e-03 (-0.09,  0.08)
Time2 * Block1                    |      0.02 (-0.02,  0.06) |      0.02 (-0.02,  0.06)
Group2 * Switch1                  |      0.02 (-0.04,  0.08) |      0.02 (-0.04,  0.08)
Time2 * Switch1                   | -4.22e-03 (-0.04,  0.04) | -4.22e-03 (-0.04,  0.04)
Group2 * Time2 * Block1           |      0.50 ( 0.45,  0.56) |      0.50 ( 0.45,  0.56)
Group2 * Time2 * Switch1          |      0.06 ( 0.00,  0.12) |      0.06 ( 0.00,  0.12)
Group2 * Block1 * Switch1         |      0.05 (-0.03,  0.12) |                         
Block1 * Switch1                  |     -0.26 (-0.32, -0.20) |                         
Group2 * Time2 * Block1 * Switch1 |     -0.12 (-0.23, -0.01) |                         
Time2 * Block1 * Switch1          |      0.04 (-0.04,  0.12) |                         
Group2 * Switch1 * Block1         |                          |      0.05 (-0.03,  0.12)
Switch1 * Block1                  |                          |     -0.26 (-0.32, -0.20)
Group2 * Time2 * Switch1 * Block1 |                          |     -0.12 (-0.23, -0.01)
Time2 * Switch1 * Block1          |                          |      0.04 (-0.04,  0.12)
---------------------------------------------------------------------------------------
Observations                      |                    11769 |                    11769

VarCorr(model7)

 Groups   Name        Std.Dev. Corr                
 Subj     (Intercept) 0.175990                     
          Time2       0.136619 -0.370              
          Block1      0.123200  0.119 -0.768       
          Switch1     0.067065 -0.052  0.160  0.025
 Item     (Intercept) 0.020960                     
 Residual             0.381140

VarCorr(model13)

 Groups   Name        Std.Dev. Corr                
 Subj     (Intercept) 0.175975                     
          Time2       0.136613 -0.370              
          Switch1     0.067048 -0.052  0.161       
          Block1      0.123195  0.119 -0.768  0.025
 Item     (Intercept) 0.020951                     
 Residual             0.381140

RK: There is no difference due to different order of factors here. The problem in original code was perhaps the false-positive convergence error that is no longer present in model7 with control=lmerControl(calc.derivs=FALSE).

7.4 Regression diagnostics for model13

hist(resid(model13))

qqPlot(resid(model13))

[1] 10623  8968

qplot(x=fitted(model13), y=resid(model13), geom="point",  shape=I("."), 
      xlab="Fitted values", ylab="Standardized residuals") + 
  geom_hline(yintercept=0) + theme_bw() + geom_hex() + geom_density2d(size=1)

8 RK’s proposal

8.1 Contrasts and indicator variables

contrasts(dat$Group)   <- contr.sum(2)
contrasts(dat$Time)    <- contr.sum(2)
contrasts(dat$Block)   <- contr.sum(2)
contrasts(dat$Switch)  <- contr.sum(2)
contrasts(dat$Task)    <- contr.sum(2)
contrasts(dat$Valence) <- contr.sum(2)


mm <- model.matrix(~ 1 + Group*Time*Block*Switch + Task*Valence, data=dat)
gr <- mm[,2]
tm <- mm[,3]
bl <- mm[,4]
sw <- mm[,5] 
tk <- mm[,6]
vc <- mm[,7]

8.2 Model selection

8.2.1 Maximal LMM `m_max`

I use MixedModels.jl in script Cajar_IAT_Julia.qmd to demonstrate model selection starting with a maximal LMM (relative to the experimental design, that is without inclusion of covariates such as trial number, subject age, or items’ frequency), but including also the two item factors Task and Valence.

m_max <- lmer(speed ~  1 + Group*Time*Block*Switch*Task*Valence +
                     (1 +       Time*Block*Switch*Task*Valence | Subj) +  
                     (1 + Group*Time*Block*Switch              | Item),
             data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))

With this model we estimate the maximal number of fixed effects (2^6 = 64 terms) and their corresponding VCs and CPs for Subj and for Item grouping variables, that is we estimate variance components (VCs) and correlation parameters (CPs) for within-subject factors for Subj (i.e., 2^5 = 32 VCs and 32 x 31 /2 = 496 CPs) and for within-item factors for Item (i.e., 2^4 = 16 VCs and 16 x 15 /2 = 120 CPs), plus the observation-level residual variance. Thus, 64+(32+496)+(16+120)+1=729 model parameters are estimated from 11679 observations. Given 38 subjects and 20 items, there are also 38 subject x 32 parameters + 20 items x 16 parameters = 1536 conditional means of the random effects for the two random factors.

I was not able to fit this LMM with lme4::lmer().

8.2.2 Selected LMM `m1`

Model selection led to the model refit here.

f_m1 <- "./fits/m1.rda"
if(!file.exists(f_m1)){
  m1 <- lmer(speed ~ 1 + gr*tm*bl*sw + tk*vc + 
                    (1 +    tm+bl+tm:bl |Subj) + 
                    (0+sw+tk+vc + tm:vc + bl:sw + bl:vc  || Subj) +
                    (1 + bl || Item), 
             data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
  save(m1, file=f_m1)
} else {
  load(f_m1)
}
summary(rePCA(m1))

$Subj
Importance of components:
                         [,1]   [,2]    [,3]    [,4]    [,5]    [,6]    [,7]
Standard deviation     0.4445 0.2771 0.10119 0.08645 0.08299 0.08198 0.07486
Proportion of Variance 0.6106 0.2372 0.03164 0.02309 0.02128 0.02076 0.01731
Cumulative Proportion  0.6106 0.8477 0.87938 0.90247 0.92375 0.94451 0.96183
                          [,8]    [,9]   [,10]
Standard deviation     0.07157 0.06322 0.05689
Proportion of Variance 0.01583 0.01235 0.01000
Cumulative Proportion  0.97765 0.99000 1.00000

$Item
Importance of components:
                          [,1]    [,2]
Standard deviation     0.05471 0.04378
Proportion of Variance 0.60971 0.39029
Cumulative Proportion  0.60971 1.00000

print(summary(m1), cor=FALSE)

Linear mixed model fit by maximum likelihood  ['lmerMod']
Formula: speed ~ 1 + gr * tm * bl * sw + tk * vc + (1 + tm + bl + tm:bl |  
    Subj) + ((0 + sw | Subj) + (0 + tk | Subj) + (0 + vc | Subj) +  
    (0 + vc:tm | Subj) + (0 + sw:bl | Subj) + (0 + vc:bl | Subj)) +  
    ((1 | Item) + (0 + bl | Item))
   Data: dat
Control: lmerControl(calc.derivs = FALSE)

     AIC      BIC   logLik deviance df.resid 
 10711.0  10991.2  -5317.5  10635.0    11731 

Scaled residuals: 
    Min      1Q  Median      3Q     Max 
-4.1861 -0.6266  0.0077  0.6757  3.8008 

Random effects:
 Groups   Name        Variance  Std.Dev. Corr             
 Subj     (Intercept) 0.0268745 0.16393                   
          tm          0.0046554 0.06823  -0.02            
          bl          0.0038563 0.06210   0.20 -0.77      
          tm:bl       0.0039016 0.06246  -0.03  0.81 -0.78
 Subj.1   sw          0.0010242 0.03200                   
 Subj.2   tk          0.0014032 0.03746                   
 Subj.3   vc          0.0009437 0.03072                   
 Subj.4   vc:tm       0.0005476 0.02340                   
 Subj.5   sw:bl       0.0004435 0.02106                   
 Subj.6   vc:bl       0.0007020 0.02649                   
 Item     (Intercept) 0.0004102 0.02025                   
 Item.1   bl          0.0002626 0.01620                   
 Residual             0.1370301 0.37018                   
Number of obs: 11769, groups:  Subj, 38; Item, 20

Fixed effects:
             Estimate Std. Error t value
(Intercept)  1.424988   0.027194  52.401
gr           0.018136   0.026814   0.676
tm           0.025280   0.011587   2.182
bl           0.073027   0.011242   6.496
sw           0.188681   0.006232  30.276
tk          -0.007346   0.008313  -0.884
vc           0.004547   0.007554   0.602
gr:tm       -0.047037   0.011587  -4.059
gr:bl        0.061570   0.010642   5.786
tm:bl        0.068324   0.010697   6.387
gr:sw        0.012588   0.006232   2.020
tm:sw        0.006262   0.003441   1.820
bl:sw       -0.062314   0.004852 -12.844
tk:vc        0.003153   0.005676   0.556
gr:tm:bl    -0.062460   0.010697  -5.839
gr:tm:sw    -0.006617   0.003441  -1.923
gr:bl:sw     0.001557   0.004852   0.321
tm:bl:sw     0.002808   0.003442   0.816
gr:tm:bl:sw -0.007893   0.003442  -2.293

There is no evidence for fixed efffects of word characteristics on response speed, but there are reliable individual differences associated with them.

8.3 Diagnostics for model `m1`

Using an easystats function from the {performance} package.

check_model(m1)

Could not compute standard errors from random effects for diagnostic
  plot.

The diagnostics look fine.

8.4 Plot of switch costs for speed scores

switch_costs <- dat |> 
  group_by(Time, Group, Block, Switch)|>
  summarise(M = mean(speed), SD=sd(speed), N=n(), SE=SD/sqrt(N))

`summarise()` has grouped output by 'Time', 'Group', 'Block'. You can override
using the `.groups` argument.

fig_speed <- 
  switch_costs |> 
  ggplot(aes(x=Switch, y=M, color=Block)) +
  geom_point(size=2) +
  geom_line(size=0.7, aes(group=Block)) +
  geom_errorbar(aes(ymin=M-2*SE, ymax=M+2*SE), width=.1, size=0.7) +
  scale_colour_manual("Block", values=cbPalette) +
  facet_grid(Group~Time) +
  labs(x="Task switch", y="Response speed [1/s]") +
  theme_bw(base_size=13) + theme(legend.position = "top")

8.5 Partial effect plot

For this you need the {remef} package: https://github.com/hohenstein/remef

# install.packages("devtools")
devtools::install_github("hohenstein/remef")

A more recent alternative with more options appears to be the {modelbased} package to compute marginal means. However, I have not worked with the package myself. So I stick with our own package for now.

library(remef)


Attaching package: 'remef'

The following object is masked from 'package:insight':

    has_intercept

The following object is masked from 'package:purrr':

    partial

dat$pe_ia <- remef(m1, ran="all")

# Plot partial-effect switch costs 

pe_switch_costs <- dat |> 
  group_by(Time, Group, Block, Switch)|>
  summarise(M = mean(pe_ia), SD=sd(pe_ia), N=n(), SE=SD/sqrt(N))

`summarise()` has grouped output by 'Time', 'Group', 'Block'. You can override
using the `.groups` argument.

pe_fig_speed <- ggplot(pe_switch_costs, aes(x=Switch, y=M, color=Block)) +
  geom_point(size=2) +
  geom_line(size=0.7, aes(group=Block)) +
  geom_errorbar(aes(ymin=M-2*SE, ymax=M+2*SE), width=.1, size=0.7) +
  scale_colour_manual("Block", values=cbPalette) +
  facet_grid(Group~Time) +
  labs(x="Task switch", y="Partial effects on response speed [1/s]") +
  theme_bw(base_size=13) + theme(legend.position = "top")

plots(fig_speed, pe_fig_speed, n_columns=1, tags=c("A", "B"), 
      title="Comparison of zero-order (A) and partial effects (B) in response speed")

For typical balanced experimental designs zero-order and partial-effect plots will not differ much. This is much more relevant when correlated covariates and associated interactions are part of the model.

9 Conditional means of random effects

In this section we examine much under-appreciated information estimated in LMMs, that is predictions based on model parameters for subjects and items (i.e., for units of grouping variables/levels of random factors).

9.1 Subject-related conditional means of random experimental effects

The CP’s suggest that individual differences in Time and Block effects are highly negatively correlated and individual differences in the Time x Block interaction also correlate very highly with individual differences in Time (positive) and Block (negative). Such large correlations of effects are often due to some type of artefact. They are not necessarily a “problem”, but they should be “understood” and therefore be examined in some detail. We can visualize these CPs with caterpillar plots of subjects’ conditional means of random experimental effects.

cm_m1 <- ranef(m1, drop=TRUE, condVar=TRUE, whichel="Subj")

cm_m1 <- 
  as_tibble(cm_m1) |> 
  rename(Term=term, Subj=grp) |> 
  mutate(Term = fct_recode(Term, GM = "(Intercept)", Time="tm", Block="bl",
                           Switch="sw", TxB = "tm:bl", Task="tk", Valence="vc"),
         Term = fct_relevel(Term, "Switch", after=1)) |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  droplevels()

# add subject info
cm_m1 <- 
  cm_m1 |> 
  left_join(sinfo, by="Subj") |> 
  select(Group, Subj, age, Gender, Term, condval, condsd)

# Default: Subj ordered by GM ...
cm_m1 |> 
  ggplot(aes(y=Subj, x=condval, group=Group, color=Group)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Group", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

Not that much clustering by group is visible in the default ordering by GM. How about when we order by the effect of Time? We also ignore effects associated with Task and Valence for now.

# Subj ordered by ...
ord_subj <- cm_m1 |> filter(Term=="Time") |> arrange(condval) |> pull(Subj)

# check clustering by Group
cm_m1 |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Group, color=Group)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Group", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

First, now we can see the correlation parameters in the alignments of orientations of Time, Block, and TxB.

Second, there are clear clustering effects of instruction. The instruction to fake in the retest slowed down a cluster of six subjects beyond the Time main effect. There are also six subjects who were not slowed down as much as expected from the main effect of Time. In other words, the instruction generated much between-subject variance in the faking group.

The same relatively slow subjects show the reverse effect also for the main effect of Block, that is for them the speed difference between incompatible and compatible blocks was especially large or small, respectively. The reverse effect also holds for four of the six relatively fast subjects.

Finally, for the same subsets of clusters of subjects, TxB interaction effect was especially small and large, respectively. The interaction translates into a congruency effect of Block and Switch, that is into the difference between mean of compatible/no-switch and incompatible/switch and mean of compatible/switch and incompatible no switch conditions.

We can also order subject-related Switch costs.

# Subj ordered by ...
ord_subj <- cm_m1 |> filter(Term=="Switch") |> arrange(condval) |> pull(Subj)

# check clustering by Group
cm_m1 |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Group, color=Group)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Group", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

In general, the instruction to fake does not reveal a distinct clustering of switch costs by instruction for between-subject differences. One exception might be subject S053 who showed the smallest difference in response speed between switch and no-switch trials relative to the main effect of Switch. This could have resulted from deliberate slowing of no-switch trials.

9.2 Subject-related conditional means of random quasi-experimental effects

Plots of conditional means can also be used to check for potential confounding of clustering related to Gender and age, that is of covariates not included in the LMM.

# check clustering by Gender
cm_m1 |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Gender, color=Gender)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Gender", values=cbPalette)+
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

# check clustering by Age
cm_m1 |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  mutate(Age = fct_rev(ifelse(age > median(age), "old", "young"))) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Age, color=Age)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Age group", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

# Subj ordered by ...
ord_subj <- cm_m1 |> filter(Term=="GM") |> arrange(condval) |> pull(Subj) 

cm_m1 |> 
  mutate(Age = fct_rev(ifelse(age > median(age), "old", "young"))) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Age, color=Age)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Age group (median)", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

Older subjects are slower overall and show a smaller change from baseline to retest (see GM and Time). For other effects, their credibility intervals mostly cross the zero line.

9.3 Add `age` as covariate to model `m1`

We refit the model including age (centered) as an additional covariate.

dat$age_c <- dat$age - median(dat$age)

if(!file.exists( "./fits/m1_age.rda")){
  m1_age <- lmer(speed ~ 1 + gr*tm*bl*sw + tk*vc + age_c +
                    (1 +    tm+bl+tm:bl |Subj) + 
                    (0+sw+tk+vc + tm:vc + bl:sw + bl:vc  || Subj) +
                    (1 + bl || Item), 
             data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))
  save(m1_age, file="./fits/m1_age.rda")
} else {
  load("./fits/m1_age.rda")
}
summary(rePCA(m1_age))

$Subj
Importance of components:
                         [,1]   [,2]    [,3]    [,4]    [,5]    [,6]    [,7]
Standard deviation     0.3515 0.2400 0.10118 0.08664 0.08420 0.08297 0.07190
Proportion of Variance 0.5363 0.2500 0.04444 0.03259 0.03078 0.02989 0.02244
Cumulative Proportion  0.5363 0.7863 0.83073 0.86331 0.89409 0.92398 0.94642
                          [,8]    [,9]   [,10]
Standard deviation     0.07152 0.06319 0.05686
Proportion of Variance 0.02221 0.01733 0.01403
Cumulative Proportion  0.96863 0.98597 1.00000

$Item
Importance of components:
                         [,1]    [,2]
Standard deviation     0.0546 0.04378
Proportion of Variance 0.6086 0.39137
Cumulative Proportion  0.6086 1.00000

compare_parameters(list("Selected LMM m1"=m1, "LMM m1 + age" = m1_age), 
                   effects="fixed", style="se_p")

Parameter           |       Selected LMM m1 |            LMM m1 + age
---------------------------------------------------------------------
(Intercept)         |        1.42*** (0.03) |          1.47*** (0.02)
gr                  |           0.02 (0.03) |             0.03 (0.02)
tm                  |          0.03* (0.01) |            0.03* (0.01)
bl                  |        0.07*** (0.01) |          0.07*** (0.01)
sw                  |    0.19*** (6.23e-03) |      0.19*** (6.24e-03)
tk                  |  -7.35e-03 (8.31e-03) |    -7.36e-03 (8.31e-03)
vc                  |   4.55e-03 (7.55e-03) |     4.55e-03 (7.55e-03)
gr * tm             |       -0.05*** (0.01) |         -0.05*** (0.01)
gr * bl             |        0.06*** (0.01) |          0.06*** (0.01)
tm * bl             |        0.07*** (0.01) |          0.07*** (0.01)
gr * sw             |      0.01* (6.23e-03) |        0.01* (6.24e-03)
tm * sw             |   6.26e-03 (3.44e-03) |     6.22e-03 (3.44e-03)
bl * sw             |   -0.06*** (4.85e-03) |     -0.06*** (4.85e-03)
tk * vc             |   3.15e-03 (5.68e-03) |     3.16e-03 (5.67e-03)
(gr * tm) * bl      |       -0.06*** (0.01) |         -0.06*** (0.01)
(gr * tm) * sw      |  -6.62e-03 (3.44e-03) |    -6.64e-03 (3.44e-03)
(gr * bl) * sw      |   1.56e-03 (4.85e-03) |     1.58e-03 (4.85e-03)
(tm * bl) * sw      |   2.81e-03 (3.44e-03) |     2.80e-03 (3.44e-03)
(gr * tm * bl) * sw | -7.89e-03* (3.44e-03) |   -7.89e-03* (3.44e-03)
age c               |                       | -8.52e-03*** (1.25e-03)
---------------------------------------------------------------------
Observations        |                 11769 |                   11769

param_m1_age <- 
  model_parameters(m1_age, effects="random") |> 
  pull(Coefficient)

model_parameters(m1, effects="random") |> 
  rename(Coeff_m1=Coefficient) |> 
  mutate(Coeff_m1_age=param_m1_age)

# Random Effects: Subj

Parameter             | Coeff_m1 | Coeff_m1_age
-----------------------------------------------
SD (Intercept)        |     0.16 |         0.12
SD (tm)               |     0.07 |         0.07
SD (bl)               |     0.06 |         0.06
SD (tm:bl)            |     0.06 |         0.06
SD (sw)               |     0.03 |         0.03
SD (tk)               |     0.04 |         0.04
SD (vc)               |     0.03 |         0.03
SD (vc:tm)            |     0.02 |         0.02
SD (sw:bl)            |     0.02 |         0.02
SD (vc:bl)            |     0.03 |         0.03
Cor (Intercept~tm)    |    -0.02 |        -0.33
Cor (Intercept~bl)    |     0.20 |         0.41
Cor (Intercept~tm:bl) |    -0.03 |        -0.21
Cor (tm~bl)           |    -0.77 |        -0.77
Cor (tm~tm:bl)        |     0.81 |         0.81
Cor (bl~tm:bl)        |    -0.78 |        -0.78

# Random Effects: Item

Parameter      | Coeff_m1 | Coeff_m1_age
----------------------------------------
SD (Intercept) |     0.02 |         0.02
SD (bl)        |     0.02 |         0.02

# Random Effects: Residual

Parameter         | Coeff_m1 | Coeff_m1_age
-------------------------------------------
SD (Observations) |     0.37 |         0.37

The linear trend of age is significant; other fixed effects stay significant.
Its inclusion reduces the subject-related VC for GM and increases the magnitude of associated CPs.
The quadratic trend of age was not significant (not shown).
Other VCs and CPs do not change.

We check the conditional means of random effects again using functions from easystats package {modelbased}.

cm_m1_age <- ranef(m1_age, drop=TRUE, condVar=TRUE, whichel="Subj")

cm_m1_age <- 
  as_tibble(cm_m1_age) |> 
  rename(Term=term, Subj=grp) |> 
  mutate(Term = fct_recode(Term, GM = "(Intercept)", Time="tm", Block="bl",
                           Switch="sw", TxB = "tm:bl"),
         Term = fct_relevel(Term, "Switch", after=1))

# add subject info
cm_m1_age <- 
  cm_m1_age |> 
  left_join(sinfo, by="Subj") |> 
  select(Group, Subj, age, Gender, Term, condval, condsd)

# Subj ordered by ...
ord_subj <- cm_m1_age |> filter(Term=="GM") |> arrange(condval) |> pull(Subj) 

cm_m1_age |> 
  filter(Term %in% c("GM", "Switch", "Time", "Block", "TxB")) |> 
  mutate(Age = fct_rev(ifelse(age > 45, "old", "young"))) |> 
  ggplot(aes(y=factor(Subj, levels=ord_subj), x=condval, group=Age, color=Age)) +
    geom_point() + 
    facet_grid(. ~ Term, scales="free_x") +
    geom_errorbarh(aes(xmin=condval -2*condsd,
                       xmax=condval +2*condsd), height=0) +
    scale_colour_manual("Age group", values=cbPalette) +
    geom_vline(xintercept=0) +
    xlab("Conditional mean") + ylab("Subject") +
    theme_bw() + theme(legend.position = "top")

As expected, older subjects’ conditional means for GM “moved” into the sample distribution when age is included as a covariate.

9.4 Item-related conditional means of random effects

There is only one VC for Grand Mean of speed of response by Item.
Replace item number with actual word.
Check for outliers.

Using {modelbased} with functions:

estimate_grouplevel(model, deviation=FALSE) # Group-specific effects
estimate_grouplevel(model, type="total") # BLUPs: fe + cm
reshape_grouplevel(); # CMs to wide data; then cbind() with original dataframe.
summary() for objects of reshaped_group_level()

cm_m1_item  <- 
  estimate_grouplevel(m1) |> 
  filter(Group=="Item")|>
  left_join(items, by=c("Level"="Item")) 

cm_m1_item |> 
  as_tibble() |> 
  mutate(out = if_else(Word %in% c("Liebe", "HORNISSE"), "red", "black"),
         Parameter = fct_recode(Parameter, "GM" = "(Intercept)", "Block" = "bl"),
         Word = fct_reorder(Word, Coefficient)) |> 
  ggplot(aes(y=Word, x=Coefficient, group=out, color=out)) + 
  geom_point() + 
  facet_grid(. ~ Parameter, scales="free_x", ) +
  geom_errorbarh(aes(xmin=Coefficient-2*SE, xmax=Coefficient+2*SE), height=0) +
  scale_colour_manual("", values=c("black", "red")) +
  geom_vline(xintercept=0) +
  xlab("Conditional mean") + ylab("") +
  theme_bw() + theme(legend.position = "none")

The sources of the two significant Item-related VCs of GM and Block are two items. HORNISSE (hornet) is the only item with a significantly smaller than average Block effect (see right facet; i.e., no overlap of credibility interval with zero line). Note that hornet was also the item with the numerically slowest respond speed overall (see GM, left facet). There was also one item/word that was responded to significantly faster (i.e., no overlap of credibility interval with GM) than Liebe (lover) than the Grand Mean. Makes sense.

10 Appendix

10.1 Refit `model13` with sum contrasts

In the original analysis, treatment contrasts were chosen for Group and Time because they provides a direct test of the critical cell against the average of the other three (which may be assumed to be equivalent because they do not involve fake behavior). There are four critical terms with this specification:

Interaction of Group x Time tests the critical “fake” cell against the mean of other cells.
Interaction of Group x Time x Block tests whether 1. is moderated by Block
Interaction of Group x Time x Switch tests whether 1. is moderated by Switch
Interaction of Group x Time x Block x Switch tests whether 2. and 3. are additive.

Theoretically critical interactions are: 2, 3, and 4. Interestingly, these interactions should yield the same test statistics if all four factors are specified with sum contrasts. In this respect, sum contrasts are ok.

contrasts(dat$Group) <- contr.sum(2)/2
contrasts(dat$Time)  <- contr.sum(2)/2
contrasts(dat$Block) <- contr.sum(2)/-2
contrasts(dat$Switch) <-contr.sum(2)/-2

model12_sum <- lmer(speed ~ 1 + Group*Time*Block*Switch + (1|Subj) + (1|Item), 
                data=dat, REML=FALSE, control=lmerControl(calc.derivs=FALSE))

fe_ord <- c(6, 12, 13, 16, 1:5, 7:11, 14, 15)

tibble(Parameter=names(fixef(model12)), 
       "t w/ trt"=summary(model12)$coefficients[,3], 
       "t w/ sum"=summary(model12_sum)$coefficients[,3],
       "b w/ trt"=summary(model12)$coefficients[,1], 
       "b w/ sum"=summary(model12_sum)$coefficients[,1])[fe_ord,]

# A tibble: 16 × 5
   Parameter                   `t w/ trt` `t w/ sum` `b w/ trt` `b w/ sum`
   <chr>                            <dbl>      <dbl>      <dbl>      <dbl>
 1 Group2:Time2                   -13.2      -13.2     -0.192      -0.192 
 2 Group2:Time2:Block1             17.3       17.3      0.504       0.504 
 3 Group2:Time2:Switch1             2.17       2.17     0.0633      0.0633
 4 Group2:Time2:Block1:Switch1     -2.20      -2.20    -0.128      -0.128 
 5 (Intercept)                     36.9       52.4      1.42        1.42  
 6 Group2                           1.08       0.697    0.0585      0.0374
 7 Time2                            4.45       6.87     0.0459      0.0500
 8 Block1                         -19.2      -20.0     -0.280      -0.146 
 9 Switch1                        -27.2      -51.3     -0.396      -0.374 
10 Group2:Block1                   -0.269    -16.9     -0.00552    -0.246 
11 Time2:Block1                     1.07     -18.8      0.0221     -0.274 
12 Group2:Switch1                   0.990     -3.57     0.0204     -0.0520
13 Time2:Switch1                   -0.385     -1.63    -0.00794    -0.0237
14 Block1:Switch1                  -8.92     -17.0     -0.260      -0.248 
15 Group2:Block1:Switch1            1.18       0.540    0.0484      0.0157
16 Time2:Block1:Switch1             0.984      0.807    0.0406      0.0235

Good. Expectations were met perfectly!

All other fixed-effect test statistics will depend on the chosen contrasts. In general, as sum contrasts are orthogonal, they should have better statistical power for the detection of significant main effects and other interactions than treatment contrasts. For example, the Block x Switch is of theoretical interest, too. For this interaction, with contr.sum, t = -17.0, with contr.treatment t=-8.9, despite averaging over Group and Time in this case in both models. Other fixed effects have a different meaning in the two analyses; they do not refer to the same effects! Therefore, test statistics are not comparable.

10.2 Session info

sessionInfo()

R version 4.2.1 (2022-06-23)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.5.1

Matrix products: default
LAPACK: /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] remef_1.0.7         ellipse_0.4.3       GGally_2.1.2       
 [4] car_3.1-0           carData_3.0-5       lme4_1.1-30        
 [7] Matrix_1.4-1        report_0.5.5        see_0.7.2          
[10] correlation_0.8.2   modelbased_0.8.5    effectsize_0.7.0.5 
[13] parameters_0.18.2   performance_0.9.2   bayestestR_0.12.1.2
[16] datawizard_0.5.1    insight_0.18.2      easystats_0.5.2    
[19] forcats_0.5.2       stringr_1.4.1       dplyr_1.0.9        
[22] purrr_0.3.4         readr_2.1.2         tidyr_1.2.0        
[25] tibble_3.1.8        ggplot2_3.3.6       tidyverse_1.3.2    
[28] arrow_9.0.0        

loaded via a namespace (and not attached):
 [1] TH.data_1.1-1       googledrive_2.0.0   minqa_1.2.4        
 [4] colorspace_2.0-3    ellipsis_0.3.2      estimability_1.4.1 
 [7] fs_1.5.2            rstudioapi_0.14     farver_2.1.1       
[10] hexbin_1.28.2       ggrepel_0.9.1       bit64_4.0.5        
[13] fansi_1.0.3         mvtnorm_1.1-3       lubridate_1.8.0    
[16] xml2_1.3.3          codetools_0.2-18    splines_4.2.1      
[19] robustbase_0.95-0   knitr_1.40          jsonlite_1.8.0     
[22] nloptr_2.0.3        broom_1.0.1         dbplyr_2.2.1       
[25] compiler_4.2.1      httr_1.4.4          emmeans_1.8.0      
[28] backports_1.4.1     assertthat_0.2.1    fastmap_1.1.0      
[31] gargle_1.2.0        cli_3.3.0           htmltools_0.5.3    
[34] tools_4.2.1         coda_0.19-4         gtable_0.3.1       
[37] glue_1.6.2          Rcpp_1.0.9          cellranger_1.1.0   
[40] vctrs_0.4.1         nlme_3.1-159        xfun_0.32          
[43] rvest_1.0.3         lifecycle_1.0.1     googlesheets4_1.0.1
[46] DEoptimR_1.0-11     MASS_7.3-58.1       zoo_1.8-10         
[49] scales_1.2.1        hms_1.1.2           sandwich_3.0-2     
[52] qqplotr_0.0.5       RColorBrewer_1.1-3  yaml_2.3.5         
[55] reshape_0.8.9       stringi_1.7.8       boot_1.3-28        
[58] rlang_1.0.5         pkgconfig_2.0.3     evaluate_0.16      
[61] lattice_0.20-45     patchwork_1.1.2     htmlwidgets_1.5.4  
[64] labeling_0.4.2      bit_4.0.4           tidyselect_1.1.2   
[67] plyr_1.8.7          magrittr_2.0.3      R6_2.5.1           
[70] generics_0.1.3      multcomp_1.4-20     DBI_1.1.3          
[73] mgcv_1.8-40         pillar_1.8.1        haven_2.5.1        
[76] withr_2.5.0         survival_3.4-0      abind_1.4-5        
[79] modelr_0.1.9        crayon_1.5.1        utf8_1.2.2         
[82] tzdb_0.3.0          rmarkdown_2.16      grid_4.2.1         
[85] readxl_1.4.1        isoband_0.2.5       reprex_2.0.2       
[88] digest_0.6.29       xtable_1.8-4        munsell_0.5.0